Too much foam/head (recent problem)

I've got an odd problem.

I have two kegs connected to to same regulator, set at 12psi and at a temp of 36F. Both liquid lines are 3/16" ID and about 4.5' long and the taps are about a foot above the center of the kegs.

One beer is a trappist ale (10% ABV) and the other is a Hefe (5%). Both used to pour great. Now for the last couple of weeks the trappist pours the same as it always has and the Hefe is half foam/head that doesn't dissipate much.

Nothing has changed in the system that I'm aware of, other than the amount of beer in the kegs. They're both around 1/4 full, but the Hefe may be a little lower.

Any idea what might be going on?

Well, I can't figure this one out.

I pulled the dip tube to make sure it wasn't blocked with something that was causing turbulence. It looked clean. I sanitized it and reinstalled it. The only thing I couldn't check was the dip tubes fit against the dimple in the bottom of the keg, but that shouldn't have changed since I first kegged the beer.

Next I checked the fitting at the top of the keg and didn't find any issues. Then I took the faucet apart and didn't find anything there.

Then I poured the beer on the same regulator that wasn't giving me a problem and noticed that it now has too much head.

So, I thought my gauge might be bad. I let the kegs stabilize a while and checked the keg pressure with a second gauge and it read the same as the first.

I dumped the pressure out of the kegs with the relief valve and lowered the serving pressure and was able to get a decent pour.

The thing I can't figure out is what went wrong. As far as I can tell my lines are the right length and I should be able to leave the regulator set at 12 psi and not have a problem.

Any ideas?